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  <!--*********************************************************************-->
  <h1>Hacking on Clang</h1>
  <!--*********************************************************************-->
  
  <p>This document provides some hints for how to get started hacking
  on Clang for developers who are new to the Clang and/or LLVM
  codebases.</p>
    <ul>
      <li><a href="#docs">Developer Documentation</a></li>
      <li><a href="#debugging">Debugging</a></li>
      <li><a href="#testing">Testing</a></li>
      <ul>
	    <li><a href="#testingNonWindows">Testing on Unix-like Systems</a></li>
	    <li><a href="#testingWindows">Testing using Visual Studio on Windows</a></li>
	  </ul>
      <li><a href="#patches">Creating Patch Files</a></li>
      <li><a href="#irgen">LLVM IR Generation</a></li>
    </ul>
    
  <!--=====================================================================-->
  <h2 id="docs">Developer Documentation</h2>
  <!--=====================================================================-->
  
  <p>Both Clang and LLVM use doxygen to provide API documentation. Their
  respective web pages (generated nightly) are here:</p>
    <ul>
      <li><a href="http://clang.llvm.org/doxygen">Clang</a></li>
      <li><a href="http://llvm.org/doxygen">LLVM</a></li>
    </ul>
      
  <p>For work on the LLVM IR generation, the LLVM assembly language
  <a href="http://llvm.org/docs/LangRef.html">reference manual</a> is
  also useful.</p>

  <!--=====================================================================-->
  <h2 id="debugging">Debugging</h2>
  <!--=====================================================================-->
  
  <p>Inspecting data structures in a debugger:</p>
    <ul>
      <li>Many LLVM and Clang data structures provide
        a <tt>dump()</tt> method which will print a description of the
        data structure to <tt>stderr</tt>.</li>
      <li>The <a href="docs/InternalsManual.html#QualType"><tt>QualType</tt></a>
      structure is used pervasively. This is a simple value class for
      wrapping types with qualifiers; you can use
      the <tt>isConstQualified()</tt>, for example, to get one of the
      qualifiers, and the <tt>getTypePtr()</tt> method to get the
      wrapped <tt>Type*</tt> which you can then dump.</li>
    </ul>
  
  <!--=====================================================================-->
  <h2 id="testing">Testing</h2>
  <!--=====================================================================-->
  
  <p><i>[Note: The test running mechanism is currently under revision, so the
  following might change shortly.]</i></p>
  
  <!--=====================================================================-->
  <h3 id="testingNonWindows">Testing on Unix-like Systems</h3>
  <!--=====================================================================-->
  
  <p>Clang includes a basic regression suite in the tree which can be
  run with <tt>make test</tt> from the top-level clang directory, or
  just <tt>make</tt> in the <em>test</em> sub-directory.
  <tt>make VERBOSE=1</tt> can be used to show more detail
  about what is being run.</p>

  <p>The tests primarily consist of a test runner script running the compiler
  under test on individual test files grouped in the directories under the
  test directory.  The individual test files include comments at the
  beginning indicating the Clang compile options to use, to be read
  by the test runner. Embedded comments also can do things like telling
  the test runner that an error is expected at the current line.
  Any output files produced by the test will be placed under
  a created Output directory.</p>
  
  <p>During the run of <tt>make test</tt>, the terminal output will
  display a line similar to the following:</p>
  
  <ul><tt>--- Running clang tests for i686-pc-linux-gnu ---</tt></ul>
  
  <p>followed by a line continually overwritten with the current test
  file being compiled, and an overall completion percentage.</p>
  
  <p>After the <tt>make test</tt> run completes, the absence of any
  <tt>Failing Tests (count):</tt> message indicates that no tests
  failed unexpectedly.  If any tests did fail, the
  <tt>Failing Tests (count):</tt> message will be followed by a list
  of the test source file paths that failed.  For example:</p>

  <tt><pre>
  Failing Tests (3):
      /home/john/llvm/tools/clang/test/SemaCXX/member-name-lookup.cpp
      /home/john/llvm/tools/clang/test/SemaCXX/namespace-alias.cpp
      /home/john/llvm/tools/clang/test/SemaCXX/using-directive.cpp
  </pre></tt>

  <p>If you used the <tt>make VERBOSE=1</tt> option, the terminal
  output will reflect the error messages from the compiler and
  test runner.</p>

  <p>The regression suite can also be run with Valgrind by running
  <tt>make test VG=1</tt> in the top-level clang directory.</p>

  <p>For more intensive changes, running
  the <a href="http://llvm.org/docs/TestingGuide.html#testsuiterun">LLVM
  Test Suite</a> with clang is recommended. Currently the best way to
  override LLVMGCC, as in: <tt>make LLVMGCC="clang -std=gnu89"
  TEST=nightly report</tt> (make sure <tt>clang</tt> is in your PATH or use the
  full path).</p>
  
  <!--=====================================================================-->
  <h3 id="testingWindows">Testing using Visual Studio on Windows</h3>
  <!--=====================================================================-->

  <p>The cmake build tool is set up to create Visual Studio project files
  for running the tests, "clang-test" being the root.
  Unfortunately, the test runner scripts presently don't work on Windows.
  This will be fixed during the test runner revision in progress.</p>
  
  <p>Note that the current and coming revised test runner is based on
  Python, which must be installed.  Find Python at:
  <a href="http://www.python.org/download">http://www.python.org/download</a>.
  Download the latest stable version (2.6.2 at the time of this writing).</p>
  
  <p>The GnuWin32 tools are also necessary for running the tests.
  (Note that the grep from MSYS or Cygwin doesn't work with the tests
  because of embedded double-quotes in the search strings.  The GNU
  grep does work in this case.)
  Get them from <a href="http://getgnuwin32.sourceforge.net">
  http://getgnuwin32.sourceforge.net</a>.</p>

  <!--=====================================================================-->
  <h2 id="patches">Creating Patch Files</h2>
  <!--=====================================================================-->

  <p>To return changes to the Clang team, unless you have checkin
  privileges, the prefered way is to send patch files to the
  cfe-commits mailing list, with an explanation of what the patch is for.
  Or, if you have questions, or want to have a wider discussion of what
  you are doing, such as if you are new to Clang development, you can use
  the cfe-dev mailing list also.
  </p>
  
  <p>To create these patch files, change directory
  to the llvm/tools/clang root and run:</p>
  
  <ul><tt>svn diff (relative path) >(patch file name)</tt></ul>

  <p>For example, for getting the diffs of all of clang:</p>
  
  <ul><tt>svn diff . >~/mypatchfile.patch</tt></ul>

  <p>For example, for getting the diffs of a single file:</p>
  
  <ul><tt>svn diff lib/Parse/ParseDeclCXX.cpp >~/ParseDeclCXX.patch</tt></ul>

  <p>Note that the paths embedded in the patch depend on where you run it,
  so changing directory to the llvm/tools/clang directory is recommended.</p>

  <!--=====================================================================-->
  <h2 id="irgen">LLVM IR Generation</h2>
  <!--=====================================================================-->

  <p>The LLVM IR generation part of clang handles conversion of the
    AST nodes output by the Sema module to the LLVM Intermediate
    Representation (IR). Historically, this was referred to as
    "codegen", and the Clang code for this lives
    in <tt>lib/CodeGen</tt>.</p>
  
  <p>The output is most easily inspected using the <tt>-emit-llvm</tt>
    option to clang (possibly in conjunction with <tt>-o -</tt>). You
    can also use <tt>-emit-llvm-bc</tt> to write an LLVM bitcode file
    which can be processed by the suite of LLVM tools
    like <tt>llvm-dis</tt>, <tt>llvm-nm</tt>, etc. See the LLVM
    <a href="http://llvm.org/docs/CommandGuide/">Command Guide</a>
    for more information.</p>

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